Arrangement for reducing power dissipation in a line driver

ABSTRACT

To reduce power dissipation in a line driver ( 2 ) connected to a transmission line ( 3 ) for transmitting multitone signals in the form of successive symbols separated by cyclic prefixes, generated by a digital signal processor ( 1 ), a controllable voltage supply ( 5 ) is connected with its output terminal to a supply voltage terminal ( 6 ) of the line driver ( 2 ) to supply a controllable supply voltage thereto, and with its control input terminal to a control output terminal of the digital signal processor ( 1 ). In response to an expected peak-to-peak value of the next symbol to be transmitted, the digital signal processor ( 1 ) controls the controllable voltage supply ( 5 ) during each cyclic prefix to set the supply voltage to the line driver ( 2 ).

TECHNICAL FIELD

[0001] The invention relates generally to line drivers, and morespecifically to an arrangement for reducing power dissipation in linedrivers connected to transmission lines in multitone systems, such ase.g. ADSL (Asymmetric Digital Subscriber Line) systems.

BACKGROUND OF THE INVENTION

[0002] In a multitone system, such as an ADSL-system, data informationis randomly coded into the phase and amplitude of a plurality of sinetones that are transmitted by line drivers on transmission lines inbursts with a so-called symbol rate or length, which in the ADSL case is246.3 μs.

[0003] To enable Fourier transformations to be made on each symbol, aso-called cyclic prefix is inserted between the symbols. The cyclicprefix does not contain any valid data but ensures that the multitonesignal appears continuous for the Fourier transformation.

[0004] In the ADSL case, each cyclic prefix has a length of 32 samplesor about 15 μs.

[0005] Since the phase and amplitude of each individual tone can be seenas random and the total signal consists of a sum of many tones, therewill be a great difference between successive symbols in thepeak-to-peak voltage of the total signal that is to be transmitted.

[0006] In view hereof, in normal ADSL systems, the supply voltage of theline drivers that are connected to the transmission line fortransmitting such multitone signals must be selected such that thetheoretical maximum peak can be transmitted without being clipped.

[0007] This causes the supply voltage of the line driver to be far toohigh for the majority of the symbols that are transmitted.

[0008] Consequently, the power dissipation in the line driver will behigher than necessary for most of the symbols.

SUMMARY OF THE INVENTION

[0009] The object of the invention is to bring about an arrangement forreducing the power dissipation in such line drivers.

[0010] This is attained essentially in that the supply voltage to theline driver is controlled from symbol to symbol during the cyclicprefixes in response to a known expected peak-to-peak value of the nextsymbol to be transmitted.

[0011] By adapting the supply voltage to expected peak-to-peak values,the power dissipation will be reduced in the line driver.

BRIEF DESCRIPTION OF THE DRAWING

[0012] The invention will be described more in detail below withreference to the appended drawing, on which FIG. 1 schematicallyillustrates two successive symbols to be transmitted in an ADSL system,and FIG. 2 is a schematic block diagram of one end of an ADSL connectionwith an embodiment of an arrangement according to the invention.

DESCRIPTION OF THE INVENTION

[0013]FIG. 1 schematically illustrates two successive symbols S1 and S2to be transmitted in an ADSL system.

[0014] In a manner known per se, each symbol S1 and S2, is preceded by aso-called cyclic prefix CP1 and CP2, respectively.

[0015] In ADSL systems, the symbol length is 246.3 μs, while the lengthof the cyclic prefix is 32 samples or about 15 μs as already mentioned.

[0016] In FIG. 1, the peak-to-peak value of the symbol S1 is U1, whilethe peak-to-peak value of the symbol S2 equals U2, which in FIG. 1 issupposed to be a lower value than U1.

[0017] Today, the symbols S1 and S2 illustrated in FIG. 1 aretransmitted by a line driver having a constant supply voltage even ifthey actually do not require the same supply voltage in order to betransmitted without being clipped.

[0018] Thus, unnecessary power is consumed today in such line drivers.

[0019] In FIG. 2, an arrangement according to the invention for reducingthe power dissipation in a line driver is schematically illustrated.

[0020] In FIG. 2, a digital signal processor 1 is connected with itsdigital input/output terminals to corresponding output/input terminalsof an analog front end or line driver 2 connected to a transmission line3 for transmitting and receiving data information in the form of symbolsas illustrated in FIG. 1.

[0021] In a manner known per se, the line driver 2 comprises adigital-to-analog converter (not shown) for converting digital signalsfrom the digital signal processor 1 into analog signals to betransmitted as symbols in accordance with FIG. 1, and ananalog-to-digital converter (not shown) for converting analog symbolsreceived into digital signals to the digital signal processor 1.

[0022] Also in a manner known per se, the digital signal processor 1knows the peak value of the tones to be transmitted in each symbol.

[0023] Thus, the digital signal processor 1 has knowledge of the peakvalue U1 in the symbol S1 in FIG. 1 before it is transmitted to the linedriver 2 as well as of the peak value U2 in the symbol S2 in FIG. 1.

[0024] With this knowledge, the digital signal processor 1 can selectthe most appropriate supply voltage to the driver 2 for each symbol.

[0025] An embodiment of an arrangement for enabling such a supplyvoltage selection is illustrated in FIG. 2.

[0026] In the embodiment in FIG. 2, the digital signal processor 1 isconnected via a control bus 4 to a switch 5 which is adapted to applydifferent supply voltages SV1, SV2 . . . SVn to a supply voltage inputterminal 6 of the driver 2 in response to different control signals fromthe digital signal processor 1 on the control bus 4.

[0027] It should be pointed out in this connection that the differentsupply voltages do not have to be fixed and be applied by means of aswitch but can be supplied e.g. by a controllable DC/DC converter (notshown).

[0028] Anyhow, in accordance with the invention, the selection of theappropriate supply voltage to the driver 2 takes place during eachcyclic prefix CP1, CP2, i.e. at times when no relevant information istransmitted.

[0029] Thus, during each cyclic prefix, an optimum supply voltage forthe driver 2 for the next symbol to be transmitted can be selectedwithout causing any disturbances.

[0030] By optimizing the supply voltage for each symbol, the total powerdissipation of the driver 2 can be considerably reduced.

1. An arrangement for reducing power dissipation in a line driver (2)connected to a transmission line (3) for transmitting multitone signalsin the form of successive symbols (S1, S2) separated by cyclic prefixes(CP1, CP2), generated by a digital signal processor (1), characterizedin that it comprises a controllable voltage supply (5) having an outputterminal and a control input terminal, the output terminal of thecontrollable voltage supply (5) being connected to a supply voltageterminal (6) of the line driver (2) to supply a controllable supplyvoltage thereto, and the control input terminal of the controllablevoltage supply (5) being connected to a control output terminal of thedigital signal processor (1), the digital signal processor (1) beingadapted to control the controllable voltage supply (5) during eachcyclic prefix (CP1, CP2) to control the supply voltage to the linedriver (2) in response to an expected peak-to-peak value of the nextsymbol to be transmitted.
 2. The arrangement according to claim 1 ,characterized in that the controllable voltage supply (5) is connectedto the digital signal processor (1) via a control bus (4).
 3. Thearrangement according to claim 1 or 2 , characterized in that thecontrollable voltage supply comprises a switch (5) which is adapted toapply different supply voltages (SV1, SV2 . . . SVn) to the line driver(2) in response to different expected peak-to-peak values of the symbolsto be transmitted.
 4. The arrangement according to claim 1 or 2 ,characterized in that the controllable voltage supply comprises a DC/DCconverter controlled by the digital signal processor (1).